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An integer overflow can cause the value to wrap and become negative, which violates the program's assumption and may lead to unexpected behavior (for example, 8-bit integer addition of 127 + 1 results in −128, a two's complement of 128).
The problem with the code is it does not check for integer overflow on the addition operation. If the sum of x and y is greater than the maximum possible value of an unsigned int , the addition operation will overflow and perhaps result in a value less than or equal to MAX, even though the sum of x and y is greater than MAX.
Example 1: legacy code may have been designed for ASCII input but now the input is UTF-8. Example 2 : legacy code may have been compiled and tested on 32-bit architectures, but when compiled on 64-bit architectures, new arithmetic problems may occur (e.g., invalid signedness tests, invalid type casts, etc.).
On 5 January 1975, the 12-bit field that had been used for dates in the TOPS-10 operating system for DEC PDP-10 computers overflowed, in a bug known as "DATE75". The field value was calculated by taking the number of years since 1964, multiplying by 12, adding the number of months since January, multiplying by 31, and adding the number of days since the start of the month; putting 2 12 − 1 ...
Canaries or canary words or stack cookies are known values that are placed between a buffer and control data on the stack to monitor buffer overflows. When the buffer overflows, the first data to be corrupted will usually be the canary, and a failed verification of the canary data will therefore alert of an overflow, which can then be handled, for example, by invalidating the corrupted data.
Overflow cannot occur when the sign of two addition operands are different (or the sign of two subtraction operands are the same). [1] When binary values are interpreted as unsigned numbers, the overflow flag is meaningless and normally ignored. One of the advantages of two's complement arithmetic is that the addition and subtraction operations ...
In C the use of any automatic variable before it has been initialized yields undefined behavior, as does integer division by zero, signed integer overflow, indexing an array outside of its defined bounds (see buffer overflow), or null pointer dereferencing. In general, any instance of undefined behavior leaves the abstract execution machine in ...
For example, where 3 / 2 = 1, we are seeing integer underflow. The references to integer underflow are misleading. There will always be more examples of the misuse of the term integer underflow than examples of its correct use, because the proportion of material concerned with integer overflow far exceeds that concerned with integer underflow.